This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. This project will measure the folding of the transactivation response element (TAR) from HIV using small-angle X-ray scattering (SAXS). TAR forms a helix-junction-helix, a basic structural motif in RNA and the basis of RNA folding, thus providing insight into most structured RNAs. TAR is also medically relevant for its role in the lifecycle of HIV. This project will probe the structure of HIV TAR in the presence of aminoglycosides and counterions, and compare it to existing models and NMR data.